Fire extinguishing composition



United States Patent Ofifice 3,274,105 Patented Sept. 20, 1966 3,274,105 FERE EXTINGUISHING COMPOSITION Norbert Mevel, Antony, France, assignor to Societe dEtudes Chimiques pour lllndustrie ct IAgricuiture S.E.C.P.I.A., Paris, France No Drawing. Filed July 15, 1963, Ser. No. 295,213 Claims priority, application France, Aug. 3, 1962, 905,979, Patent 1,338,454 Claims. (Cl. 2522) This invention relates to fire extinguishing solutions for use against dry fires and fires particularly difiicult to extinguish such as those of hydrocarbons or inflammable chemicals and mixed fires, that is to say, fires of combustible solid substances (wood, paper, rags, etc.) soaked for example with hydrocarbons or chemicals.

It is well known that many potassium salts have interesting fire extinguishing properties and may be used either in the form of powder or in the form of aqueous solutions to fight fires. In particular, it has been proposed to use aqueous solutions of potassium acetate optionally mixed with other alkali metal salts and/or products such as wetting agents and other surface active agents which make the spraying easier. These solutions containing a relatively small quantity of potassium acetate are suitable to fight dry fires or fires generally easy to extinguish but they are not highly effective against fires of very inflammable substances such as gasoline for instance.

It is well known that as a general rule the effectiveness of a saline solution increases as the salt concentration is higher. However, when trying solutions containing more than about 300 g./l. of potassium acetate, many tests have shown that during the spraying operation a precipitation occurs due to cooling and evaporation. This makes the liquid more difficult to disperse and causes a rapid blocking of the spray nozzles through which the extinguishing solution is projected onto the fire. Thus, it is possible to put out a fairly small fire, but as the source of the fire grows, extinction becomes less certain and even totally impossible.

An object of this invention, therefore, is to provide novel and more effective fire extinguishing solutions based on potassium acetate.

Another object is to provide a method of extinguishing fires with the solutions of this invention.

It is a further object of this invention to provide a new and improved process to prepare said extinguishing solutions.

Upon further study of the specification and claims, other objects and advantages of the present invention will become apparent.

It has now been found that an excellent extinguishing effect is obtained without any risk of precipitation during the spraying by using solutions containing about 300 to about 600 g./l. of potassium acetate and having a pH value of at least 7, and preferably ranging from about 7.5 to 8.5. The upper limit of the pH is unimportant, for any higher pH is satisfactory to fight fires, but pHs lower than 8.5 are preferred so as to obtain solutions less corrosive and less sensitive to wetting agents.

When the acetate concentration exceeds 600 g./l. there is practically no improvement in extinguishing properties while the risk of precipitation reappears even though the pH is kept Within the above-mentioned limits. The risk increases as the concentration rises and gets nearer to potassium acetate saturation point which is very close to 1000 g./l. at room temperature.

It has been observed that solutions containing from about 300 to about 600 g./l. of potassium acetate, maintained at suitable pH, will very quickly extinguish fires of hydrocarbons or inflammable chemicals (excepting, however, particularly rebellious fires of sulfur compounds such as carbon disulfide and percaptans). Nevertheless, within the above-mentioned limits, it is advisable to choose the concentration of the solution according to the nature of the fires to be dealt with: for fires of high boiling hydrocarbons and those of a large number of chemicals such as alcohol, aldehydes, amines, petroleum ether, ethyl ether, etc-., solutions containing from 300 to 400 g./l. of potassium acetate give the best results. But for fires of low boiling hydrocarbons such as gasoline, solutions containing from about 500 to 600 g./l. are more effective to obtain complete extinction.

It has also been found that by adding tetrapotassium pyrophosphate to aqueous solutions of potassium acetate, the extinguishing effect is considerably increased and that the same results are obtained with a lower acetate concentration. For example, a solution containing 300 g./l. of potassium acetate to which 100 to 200 g./l. of tetrapotassium pyrophosphate have been added, has the same extinguishing effect on a gasoline fire as a solution containing about 500 g./l. of potassium acetate alone.

Solutions containing both acetate and tetrapotassium pyrophosphate have outstanding extinguishing properties on mixed fires because this latter salt gives to the combustible solid substances soaked with extinguishing liquid such fireproof qualities that the risk of re-flashing is considerably reduced or even avoided.

Although the addition of wetting agents does not better the specific extinguishing properties of the solutions disclosed in the present invention, such products added in small quantities, by reducing the surface tension of the liquid, will improve the dispersion of the droplets whereby the spraying operation is made easier. Therefore, the use of a wetting agent is mainly dependent upon the type of spraying apparatus chosen. Obviously, the wetting agent must be compatible with the dissolved salts: for example, to the solution disclosed in the present invention it is possible to add a wetting agent of oxyethylenic alkylphenol type or a phosphate ester of non-ionic compounds, preferably in quantity not exceeding 2% by weight of solution. Specific examples of such wetting agents are compounds of formula Where n is 6 to 15, R is H or CH and R an alkyl residue having 8 or 9 carbon atoms.

In addition to their excellent fire extinguishing properties, the solutions disclosed in the present invention have other outstanding advantages which are set forth herebelow.

The freezing point of concentrated potassium acetate solutions is very low, solutions containing about 600 g./l. being practically non-freezing under all climates.

It has been found that the freezing point of potassium acetate solutions first decreases as the salt concentration rises up to about 600 g./l.; but if the salt concentration continues to rise above 600 g./l., then the freezing point increases. This fact is illustrated in the table hereunder.

Salt concentration in g./l.

of potassium acetate: Freezing point C.)

The addition of tetrapotassium pyrophosphate to potassium acetate solutions does not appreciably alter the freezing points. For example, the freezing point of a solution containing 400 g./l. of acetate and 100 g./l. of pyrophosphate is close to 40 C.

The fire extinguishing solutions disclosed in the present invention can thus be stored without any danger of freezing, those having a freezing point equal or lower to -40 C. being of course selected when climatic conditions are particularly severe. The extinguishing properties of these solutions are not altered at low temperature and they remain fiuid enough to allow an effective spraying operation with a suitable device.

The fire extinguishing solutions herein set forth can be produced by any known method but a particularly simple method has been found to prepare them at low cost. According to this method, potassium acetate solutions are prepared by the action of acetic acid on a mixture of potassium carbonate and hydroxide. Thus, neutralization is reached much more quickly and more easily than by the already known and generally used processes. The known processes comprise reacting acetic acid with either potassium carbonate or potassium hydroxide, both known methods having serious drawbacks; in the first case the mixture must be heated and stirred vigorously in order to facilitate the evolution of carbon dioxide; and in the second case, a strong cooling is necessary to eliminate the heat caused by neutralization of potassium hydroxide.

The method of the present invention overcomes these various drawbacks and allows manufacture of potassium acetate without any external heating or cooling. This method consists in gradually adding a quantity of acetic acid sufficient to obtain neutralization to an aqueous solution of potassium hydroxide containing potassium car bonate, the molar ratio K CO /KOH of the mixture being in the range of 0.5:1 to 1.25:1, preferably 0.6:1 to 0.8:1. The gradual addition of acetic acid means that the whole amount of acetic acid is not added all at once to the aqueous solution of potassium hydroxide containing potassium carbonate as it would cause a too sudden evolving of carbon dioxide. To prevent this from happening the addition of acetic acid is made either step by step or continuously at a rate sufficient to obtain a steady degasifying.

When operating as described above, the temperature of the reaction mixture adjusts itself at a suitable value which is from about 95 to about 60 C., preferably close to 80-85 C. when the molar ratio K CO /KOH is comprised between 0.6:1 and 0821. Additionally, carbon dioxide evolves spontaneously without requiring any vigorous agitation for degasifying. Only .a slight stirring of the mixture is enough to obtain a slurry of potassium carbonate and to prevent it from collecting at the bottom of the reaction vessel.

According to this new method, fire extinguishing solutions can be prepared directly at the desired concentration ready for spraying onto fires. But, should the site of utilization be situated far from the manufacturing unit, it is possible to prepare highly concentrated solutions fairly close to saturation point, for instance solutions containing 800 to 1000 g./l. of potassium acetate, in order to reduce transportation costs. These solutions can also include the tetr-apotassium phosphate and/or wetting agent in the appropriate proportions, taking into account that the solutions will be eventually diluted to concentrations of less than about 600 g./l. of KAc. Besides saving transport costs, these highly concentrated solutions also have the advantage of being much less corrosive than the more dilute ones and can hence be stored and transported without any damage to the containers.

The extinguishing solutions disclosed in the present invention can be employed in any usual type of apparatus for projecting or spraying water under gas pressure.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the specification and claims in any way whatsoever.

Example 1 A highly concentrated solution of potassium acetate was prepared as follows:

171 kg. of technical grade potassium carbonate containing 96% K CO 90 kg. of potassium hydroxide containing 93% KOH, and liters of water are put into a vessel. The mixture is stirred gently just enough to maintain the potassium carbonate in suspension therein while 300 liters of acetic acid of technical grade containing 80% of CHgCOOH are gradually added; the temperature rises up to C. without external heating. At the end of the reaction 405 liters of a solution containing 900 g./l. of potassium acetate are obtained.

The solution thus obtained was used to prepare a series of more dilute solutions at pH 7.5, containing respectively 300, 400, 500 and 600 g./l. of potassium acetate with which were carried out different field tests with hydrocarbon fires under the conditions hereafter described.

For each test 20 liters of essence H (mineral spirit having a boiling range from 35 to 200 C. under normal pressure) were poured into a round pan measuring 1.50 m. diameter and 0.20 m. high. The liquid was ignited and left to burn for one minute, then the solution was projected onto the fire under 8 kg./cm. pressure through a hose nozzle, the time for complete extinction being measured. Once the fire was out, the liquid "was ignited a second time and left to burn for 30 seconds, the time required for complete extinction again being measured The same operation was carried out three times.

The following table, wherein s represents seconds, illustrates the results obtained with the different acetate solutions:

Time necessary for complete extinction Concentration of the Solution, g./l. Ignition 1st re- 2nd re- 3rd reignition ignition ignition 600 l5 s 60 s 10 s 3 s 18 s 15 s 8 s 3 s 19 s 36 s 9 s 4 s 26 s 25 s 22 s 10 5 Example 2 Laboratory tests were carried out on ethanol fires with an apparatus giving a representative and homothetic picture of field tests effected in a round pan measuring 1 m. diameter and 0.20 m. high with a horizontal bottom.

With a 300 g./l. potassium acetate solution at pH 7.2, the fire was extinguished immediately (less than one second) for first ignition as well as for the following ones. Similar results were obtained with a 500 g./l. potassium acetate solution though the extinction is even more striking, the smothering effect being instantaneous.

Moreover, it was observed that the mists of both solutions prevented the ethanol from being ignited by an electric spark.

Example 3 10 liters of gasoline, some old rags and pieces of wood were placed in a round pan measuring 0.80 m. diameter and 0.20 m. high. These substances were ignited and left to burn for two minutes, the result being that the whole stake was burning fiercely. A solution containing 300 g./l. of potassium acetate, g./l. of tetrapotassium pyrophosphate and 2% by weight of a wetting agent commonly sold under the trade-name of GAFAC RE 610 was then sprayed onto the blazing fire. It took only one second to extinguish it completely in all cases, i.e., the first ignition and the following reignitions. In fact, after the first re-ignition the wood does not catch fire again owing to the fireproof properties of tetrapotassium pyrophosphate. Moreover, no spontaneous flames reappear after the first extinguishing operation.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and Without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitable, and intended to be, Within the full range of equivalence of the following claims.

What is claimed is:

1. A method of extinguishing a fire, which method comprises the step of contacting the source of the fire with an aqueous solution containing about 300-600 grams/liter of potassium acetate and in addition a sufficient quantity of tetrapotassium pyrophosphate to increase the extinguishing eflect of said potassium acetate, said solution having a pH higher than 7.

2. The method of claim 1 wherein the concentration of potassium acetate is about 300-400 grams/liter and the concentration of tetrapotassium pyrophosphate is about 100-200 grams/ liter.

3. A method of extinguishing fires in climatic temperatures of below 40 C., which method comprises the step of, at said temperatures, contacting the source of the fire with an aqueous solution containing about 400 grams/liter of potassium acetate and about 100 grams/ liter tetrapotassium pyrophosphate, said solution having a pH higher than 7.

4. A fire extinguishing composition comprising, on the basis of a liter of aqueous solution, about 300 to about 600 grams/ liter of potassium acetate, a sufficient amount of tetrapotassium pyrophosphate to increase the extinguishing effect of said potassium acetate, and suificient water to make a liter of solution, said solution having a pH above 7.

5. A fire extinguishing composition suitable for climatic conditions below 40 C., said composition comprising, on the basis of a liter of aqueous solution, about 400 grams/liter of potassium acetate, about 100 grams/ liter of tetrapotassium pyrophosphate, and sufficient water to make a liter of solution, said solution having a pH above 7.

6. A fire extinguishing composition comprising, on the basis of a liter of aqueous solution, about 300 to about 400 grams/liter of potassium acetate, about 100 to about 200 grams/liter of tetrapotassium pyrophosphate, a wetting agent compatible with the dissolved salts in a concentration of less than 2% by Weight of the solution, and sutficient Water to make a liter of solution, said solution having a pH above 7.

7. A process for the preparation of an aqueous potas sium acetate fire extinguishing solution, which process comprises gradually adding acetic acid to an aqueous mixture of potassium carbonate and potassium hydroxide, the molar ratio K CO /KOH of the mixture being about 0.5 :1 to about 1.25:1, the quantity of acetic acid being sufficient to neutralize said mixture, said solution having a pH above 7.

8. The process of claim 7, wherein the molar ratio K CO /KOH is about 0.6:1 to about 0.8: 1.

9. The process of claim 7, wherein the concentration of potassium carbonate and potassium hydroxide in the aqueous mixture is sufl'lci'ent to yield a potassium acetate concentration of about 300-600 grams/liter.

10. The process of claim 7, wherein the concentration of potassium carbonate and potassium hydroxide in the aqueous mixture is sufiicient to yielda potassium acetate concentration of about 800-1000 grams/liter.

References Cited by the Examiner UNITED STATES PATENTS 1,936,754 11/1933 Dreyfus et al. 260-541 2,624,706 1/1953 Maxcy et al 2522 2,876,118 3/1957 Jackson et a1. 252-8.1 XR 2,895,990 7/1959 Larrison et a1. 260-541 XR OTHER REFERENCES Effect of Alkali-Metal Compounds on Combustion, Thomas et al., Industrial and Engineering Chemistry, vol. 20, June 1928, pp. 575-577.

Tetrapotassi-um Pyrophosphate, Hooker Chemical M. WEINBLATT, Assistant Examiner. 

1. A METHOD OF EXTINGUISHING A FIRE, WHICH METHOD COMPRISES THE STEP OF CONTACTING THE SOURCE OF THE FIRE WITH AN AQUEOUS SOLUTION CONTAINING ABOUT 300-600 GRAMS/LITER OF POTASSIUM ACETATE AND IN ADDITION A SUFFICIENT QUANTITY OF TETRAPOTASSIUM PYROPHOSPHATE TO INCREASE THE EXTINGUISHING EFFECT OF SAID POTASSIUM ACETATE, SAID SOLUTION HAVING A PH HIGHER THAN
 7. 7. A PROCESS FOR THE PREPARATION OF AN AQUEOUS POTASSIUM ACETATE FIRE EXTINGUISHING SOLUTION, WHICH PROCESS COMPRISES GRADUALLY ADDING ACETIC ACID TO AN AQUEOUS MIXTURE OF POTASSIUM CARBONATE AND POTASSIUM HYDROXIDE, THE MOLAR RATIO K2CO3/KOH OF THE MIXTURE BEING ABOUT 0.5:1 TO ABOUT 1.25:1, THE QUANTITY OF ACETIC ACID BEING SUFFICIENT TO NEUTRALIZE SAID MIXTURE, SAID SOLUTION HAVING A PH ABOVE
 7. 